Cyclone furnace having ash removal means

ABSTRACT

In cyclone furnaces used for burning bark and similar wood refuse, the removal of ash and cinder involves a delicate problem because the combustion residues are easily fused when subjected to elevated temperature. The commonly used openings in a grate covering an ash pit is not satisfactory to remove the rotating products, and it is now proposed to arrange an opening in the side wall of the cyclone, just above the grate, and to fit an ejector means into said opening for continuously removing the combustion residues.

[111 3,834,327 Sept. 10, 1974 United States Patent Hellstrom et al.

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mmvw mmm n m mm .mo SKM 6926 5566 9999 llll H2 ll 1 1 30 52 1 1 9729 628 7 992 2233 Karsberg, Saffle; Ingmar Astrom,

Stenungsund, all of Sweden [73] Assignee: Gotaverkens Angtekniska ABPrimary Examiner-+Kenneth W. Sprague (Gotaverken Heat EngineeringAttorney, Agent, or Firm-Holman & Stern Ltd.), Goteborg, Sweden Apr. 18,1973 [22] Filed:

[21] Appl. No.: 352,304

In cyclone furnaces used for burning bark and similar Fm'elgnAppllcatlml P110! "3' Data wood refuse, the removal of ash and cinderinvolves a June 14, 1972 Sweden.,.........................

007803/72 delicate problem because the combustion residues are easilyfused when subjected to elevated tem perature. The commonly usedopenings in a grate covering an 0 0 5/ 7 00 W8. 1F R u 9 4 0 1 1 R 8 1 01 1 L m G Sh Um nu ll ash pit is not satisfactory to remove the rotatingprod- [58] Field of Search....... /8 R ucts, and it is now proposed toarrange an opening in the side wall of the cyclone, just abo to fit anejector means into said ope 18 R, 28 F, 28 L,

ve the grate, and ning for continu- References Cited UNITED STATESPATENTS ously removing the combustion residues.

4 Claims, 3 Drawing Figures 2,627,827 2/1953 Elliot 110/165 l ll l rh lil l l Ill 3/ 4 111111 M1 l l 1 11111 villi o l: 11 v 1| 111 3 f 1 r 11|11\\/| 111111111111] ,1 Ill, ill 6 1 1 i 1 1 II II 8 3 111 iiilll l1 1O ll 1 I Iii lliiilll/ ii I 1'11 fl oil! I fl H iA P 2 7// o u/// M\\\W\\& H 1

PATENTED I 3.834.327 SHEET 20F 2 FIG. 3

0 Kso BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERREDEMBODIMENT The cyclone furnace has a cylindrical combustion For thecombustion of wood refuse such as bark 5 Chamber a vertical axis and ISprovided a chips and the like, a cyclone furnace is often used. Such afurnace comprises a cylindrical, vertical combustion chamber, which, inits lower part is provided with a grate and usually also a mechanicalstoking device feeding the fuel to the central portion thereof, in sucha manner that the fuel will form a substantially conical mound thereon.Other ways of feeding the fuel include a chute for feeding the fuel ontothe grate in a downward direction. In its upper part, the combustionchamber is provided with a number of tangentially directed air nozzles,which impart a forceful whirling motion upon the combustion gases.

The diameter of the grate is selected in such a manner with respect tothe desired combustion capacity and to the angle of repose of the fuelto be used that an annular passage, free of fuel will be formed aroundthe mound of fuel. The grate is, within this annular passage, usuallyprovided with openings forming a connection with ash collecting pocketslocated below the grate.

Due to the forceful rotation within the combustion chamber, a lot ofun-burnt particles will slide down the slopes of the mound of fuel andwill collect in the annular passage. Bark contains a rather substantialamount of mineral components, and wood refuse is often contaminated withsand which has been entrained when the logs are dragged along theground. Such incombustible matter will fuse when subjected to elevatedtemperature, and it very often happens that particles of fuel stillun-burnt falling into the annular passage will be intermingled with andfused together with the mineral particles, which leads to a clogging ofthe ash removal openings in the grate.

SUMMARY OF THE INVENTION One object of the present invention is toprovide a continuous collection of such particles as are circulatedalong this annular passage by the rotating gases and to remove them fromthe mound of fuel. The invention is characterized in an exit passageopen towards the annular passage and directed tangentially with respectto the wall of the combustion chamber, in an ejector connected to saidpassage, and in a conduit connecting the ejector with a conduitconveying air under pressure in such a manner that a continuous ejectionis obtained in the exit passage. An outlet conduit from the ejector maybe connected to the upper part of the combustion chamber, oralternatively to a combustion plant located downstream of the cyclonefurnace.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section through acyclone furnace suitable for the combustion of bark and connected to asteam boiler,

FIG. 2 shows part of a section along line II II in FIG. 1, the viewlooking in the direction of the arrows, and

FIG. 3 is a view partly in elevation and partly in cross section showinga cyclone furnace fitted to a steam boiler.

grate l 1 in its lower portion. The fuel, which on this occasionconsists of bark and similar wood refuse, is fed centrally onto thisgrate by means of a stoking apparatus 12, the details of which are notshown on the draw- 0 ing, in such a manner that a substantially conicalmound 13 will be formed upon the grate. The diameter of the grate and ofthe furnace chamber is selected in such a manner with respect to thedesired combustion capacity and the angle of repose of the fuel to beused that, during use, an annular passage 14, free of fuel, will beformed around the mound of burning fuel.

In the upper part of the combustion chamber a number of nozzles 16 forthe injection of secondary air are provided. These nozzles are directedtangentially with respect to an imaginary cylinder concentric with theaxis of rotation and are supplied with preheated air from a duct 17connected to a fan (not shown). The

combustion chamber is connected to a furnace 18 of a steam boiler, whichis indicated above the cyclone furnace.

The air issuing from the secondary air nozzles 16 induce a forcefulwhirling motion within the chamber. A great many particles of un-burntmatter are carried by this vortex and will be finally combusted carriedby the gases. A number of heavier particles will, .however, slide downalong the wall of the combustion chamber, ending up in the annularpassage, where they, while still burning, may be baked together with ashparticles sliding down along the slope of the mound of fuel and willform a sintered slag clogging the air entrance opening in the outerportion of the grate, as well as possible ash removal openings in theannular passage.

As long as the glowing particles are kept in motion they will do noharm, but if a local braking of the movement occurs, the building up ofa solid coating starts. It therefore is important that the particles arecontinuously removed.

An exit passage 19 is provided in the wall of the combustion chamber,just above the grate and is directed towards the rotating gas-swirl. Alllarger particles will be collected in this passage. The passage isconnected to an ejector 20, which, by way of a first conduit 21, isconnected to the duct 17 supplying secondary combustion air. Theparticles collected will, in this manner, by way of a second conduit 22,be transported from the ejector to the furnace of the steam boiler,downstream of the cyclone furnace, in which they will be finally burnt.The resulting ash has the consistency of light cinder, and willfacilitate the cleaning of the heating surfaces of the steam boilerwhile passing through the latter.

As indicated at 23, it is, of course possible, to connect the conduit 22to the upper part of the combustion chamber to the cyclone furnace,above the level of the secondary air nozzles 16. The final combustion ofthe collected particles will then start in the cyclone furnace, but willbe finalized in the second furnace, with the particles following the gasstream passing through the throat connecting the two furnaces.

An inspection and cleaning opening having a cover 15 is provided at theejector 20 in such a manner that the latter, as well as the exit passagemay be cleaned,

which may be brought about by means of a whisk which is periodicallyintroduced into the passage.

FIG. 3 shows the cyclone furnace l fitted to a steam boiler, thecombustion chamber 18 of which is provided with oil burners 30 or otherfuel combustion means operable independently of the cyclone furnace.

The combustion gases leaving the steam boiler will pass through a dustseparator 31 connected to the smoke stack. Conduit 22 from the ejectorat the cyclone furnace is connected to the dust separator at 32, andwill pass through a feed water heater 33 or some similar heat exchangerfor cooling of the mixture of air and ash particles.

What we claim is:

1. In a cyclone furnace having a vertical axis, a combustion chamberprovided with upper and lower portions, a grate in the lower portion ofthe combustion chamber, means for feeding solid fuel onto the grate toform, in use, a conical mound of burning matter thereon, said gratehaving such an extension in relation to the desired combustion capacityand to the angle of response of the fuel utilized that an annularpassage, free of fuel is formed around the mound, a number of nozzles inthe upper portion of the combustion chamber for the introduction ofsecondary air tangentially with respect to an imaginary cylinderconcentric with the longitudinal axis of the chamber, and an axialoutlet for the combustion gases, a gas passage to which said axialoutlet leads, the improvement including an exit passage in a side wallof the cyclone furnace located level with an open towards the annularpassage and directed tangentially away therefrom, an ejector meansfitted into said exit passage, the ejector means having an outlet end, afirst passage connecting said ejector means with a source of pressurefluid, and

a second conduit connecting the outlet end of the ejector means with thegas path downstream of the air introduction nozzles. 2. The cyclonefurnace according to claim 1, in which said source of pressure fluidsupply is the conduit conveying secondary air to the air introductionnozzles.

3. The cyclone furnace according to claim 1, in which said gas passageforms part of a heat producing plant having a smoke stack and a dustcollector connected to the smoke stack and in which the second conduitopens into said dust collector.

4. The cyclone furnace according to claim 3, including a device forcooling of the mixture of gases and solid matter therein through whichthe second conduit passes before entering the dust collector.

1. In a cyclone furnace having a vertical axis, a combustion chamberprovided with upper and lower portions, a grate in the lower portion ofthe combustion chamber, means for feeding solid fuel onto the grate toform, in use, a conical mound of burning matter thereon, said gratehaving such an extension in relation to the desired combustion capacityand to the angle of response of the fuel utilized that an annularpassage, free of fuel is formed around the mound, a number of nozzles inthe upper portion of the combustion chamber for the introduction ofsecondary air tangentially with respect to an imaginary cylinderconcentric with the longitudinal axis of the chamber, and an axialoutlet for the combustion gases, a gas passage to which said axialoutlet leads, the improvement including an exit passage in a side wallof the cyclone furnace located level with an open towards the annularpassage and directed tangentially away therefrom, an ejector meansfitted into said exit passage, the ejector means having an outlet end, afirst passage connecting said ejector means with a source of pressurefluid, and a second conduit connecting the outlet end of the ejectormeans with the gas path downstream of the air introduction nozzles. 2.The cyclone furnace according to claim 1, in which said source ofpressure fluid supply is the conduit conveying secondary air to the airintroduction nozzles.
 3. The cyclone furnace according to claim 1, inwhich said gas passage forms part of a heat producing plant having asmoke stack and a dust collector connected to the smoke stack and inwhich the second conduit opens into said dust collector.
 4. The cyclonefurnace according to claim 3, including a device for cooling of themixture of gases and solid matter therein through which the secondconduit passes before entering the dust collector.